Assessment Of The Pulmonary Genotoxicity Of Bitumen Fumes In Big Blue((R)) Transgenic Rats

Occupational and environmental exposures to bitumen fumes during road paving or roofing activities represent a safety issue since this complex mixture of volatile compounds and particles contains carcinogenic polycyclic aromatic hydrocarbons ( PAH). However, epidemiological and experimental animal studies failed to draw unambiguous conclusions concerning bitumen fumes toxicity. In order to gain better insights on their genotoxic potential, we used an experimental device able to generate bitumen fumes at 170 degrees C ( upper range used during road paving operations) with a total particulate matter of 112 +/- 13 mg/m(3) and a mass median aerodynamic diameter of 4.6 mu m. The nose- only exposure of Big Blue (R) R transgenic rats was performed 6 h/day for 5 consecutive days. Biological exposure to this aerosol was monitored by measuring the rat urinary levels of 1-hydroxypyrene and lungs were collected at various time- points after the end of treatment for further analysis. As determined by the 32P post-labeling method, no DNA bulky adduct was found in control animal lungs, while one was detected in exposed rats 3 and 30 days after the end of treatment, suggesting that this genetic alteration was rather stable. However, there was no correlation between the amount of DNA adduct and the level of urinary of 1-hydroxypyrene. The pulmonary mutagenic properties of bitumen fumes were determined by analyzing the mutation frequency and spectrum of the neutral reporter gene cII inserted into the transgenic rodent genome. Thirty days after exposure, the cII mutant frequency was similar in control and exposed rat lungs. However, a modification of the mutation spectrum was noticeable in treated animals. The most striking difference was an increase of G: C to T: A and A: T to C: G transversions in exposed rodents. In addition, the increased occurrence of G: C to T: A transversions at CpG dinucleotides in treated animals was consistent withDNAadduction by PAH. Even though these data failed to demonstrate a clear pulmonary mutagenic potential of bitumen fumes in our experimental conditions, the analysis of the mutational spectrum provides a sensitive measure of a quantitative increase of specific mutations which may be associated with DNA adduct formation. The weak mutagenic response might also be related to the small inhalable fraction of bitumen fume particles reaching the deep lung. In conclusion, these results could give insights on the mechanism of action of bitumen fumes and provide additional information concerning human risk assessment associated with bitumen exposure.